An enlarged cell technique for the conformal FDTD method to model perfectly conducting objects

A conformal finite-difference time-domain (CFDTD) method has been put forward by S. Dey and R. Mittra (see IEEE Microwave Guided Wave Lett., vol.7, p.273-5, 1997) to model curved perfectly conducting objects. The method deforms the grid locally to accommodate the curvature of the PEC surface, and therefore, avoids the staircase error of the conventional FDTD method in approximating boundaries. However, sometimes the deformed grid may be too small to obtain a stable solution. This instability can be removed by using a smaller time step, at the expense of more times steps being required. We introduce an efficient, yet accurate, technique, the enlarged cell technique (ECT), to obtain a stable solution without the need to reduce the time step (Xiao, T. and Liu, Q.H., IEEE Microwave Wireless Compon. Lett., vol.14, p.551-3, 2004). This technique has a clear geometric and physical explanation and is easy to implement. Unlike CFDTD methods, the ECT sacrifices neither accuracy nor efficiency in treating small distorted cells.